Interleukin-6 (IL-6) as a Predictor of Clinical Outcomes in Patients with COVID-19

Interleukin-6 (IL-6) has been known to be involved in immune regulation, inflammatory response, and metabolism. It is also recognized as the major cause to underscore the pathology of severe COVID-19 patients. However, it remains to be seen if IL-6 is superior to other inflammatory biomarkers in ascertaining clinical severity and mortality rate for COVID-19. This study aimed to determine the value of IL-6 as a predictor of severity and mortality in COVID-19 patients and compare it with other pro-inflammatory biomarkers in the South Asian region.

An observational study was conducted, including all adult SARS-CoV-2 patients who had undergone IL-6 testing from December 2020 to June 2021. The patients' medical records were reviewed to collect demographic, clinical, and biochemical data. Other pro-inflammatory biomarkers apart from IL-6 included Neutrophils to Lymphocyte Ratio (NLR), D-dimer, C-reactive protein (CRP), ferritin, lactate dehydrogenase (LDH), and procal-citonin for analysis. SPSS version 22.0 was utilized.

Out of the 393 patients who underwent IL-6 testing, 203 were included in the final analysis with a mean (SD) age of 61.9 years (12.9) and 70.9% (n = 144) were male. Fifty-six percent (n = 115) subjects had critical disease. IL-6 levels were elevated (> 7 pg/mL) in 160 (78.8%) patients. Levels of IL-6 significantly correlated with age, NLR, D-dimer, CRP, ferritin, LDH, length of stay, clinical severity, and mortality. All the inflammatory markers were significantly increased in critically ill and expired patients (p < 0.05). The receiver operator curve showed that IL-6 had the best area under the curve (0.898) compared to other pro-inflammatory biomarkers for mortality with comparable results for clinical severity.

Study findings show that though IL-6 is an effective marker of inflammation and can be helpful for clinicians in recognizing patients with severe COVID-19. However, we still need further studies with larger sample size.